I. Field of the Invention
The present invention relates to communication systems. More particularly, the present invention relates to a novel and improved method and apparatus for selecting a preferred communication system in a subscriber station capable of operation in a plurality of geographical regions.
II. Description of the Related Art
As mobile communication systems become more prevalent in society the demands for greater and more sophisticated service have grown. To meet the capacity needs of mobile communication systems, techniques of multiple access to a limited communication resource have been developed. The use of code division multiple access (CDMA) modulation techniques is one of several techniques for facilitating communications in which a large number of system users are present. Other multiple access communication system techniques, such as time division multiple access (TDMA) and frequency division multiple access (FDMA) are known in the art. However, the spread spectrum modulation technique of CDMA has significant advantages over these modulation techniques for multiple access communication systems.
The use of CDMA techniques in a multiple access communication system is disclosed in U.S. Pat. No. 4,901,307, issued Feb. 13, 1990, entitled "SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS", assigned to the assignee of the present invention, and is incorporated by reference herein. The use of CDMA techniques in a multiple access communication system is further disclosed in U.S. Pat. No. 5,103,459, issued Apr. 7, 1992, entitled "SYSTEM AND METHOD FOR GENERATING SIGNAL WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM", assigned to the assignee of the present invention and is incorporated by reference herein.
When the user of a subscriber station travels from one geographic area to another, the subscriber station must select a communications system upon which to conduct services. There are two means by which a user may operate his subscriber station in differing geographic regions. By the first method, the user subscribes to communications services in a variety of regions. Thus, the subscriber station needs only to seek out a communications system to which the user subscribes and may provide services using any of those service providers.
Alternatively, the user may communicate by means of roaming service. Mobile communications providers negotiate contracts among themselves to provide services known as "roaming" to their customers. A "roamer" is a subscriber station which requires service in a system which is operated by a mobile communications service provider other than the ones to which the user subscribes. Currently when a subscriber station is roaming, a signal indicative of the roaming condition is provided to the user. A roaming determination is made as a result of a comparison of the system identification (SID) of the subscribed system or systems with the SID of the system providing service which is broadcast by that system. This alerts the user of the subscriber station that the service being provided is accruing roaming charges.
Because the subscriber station is generally without knowledge of the user's geographic location, it must select the system (from the possible communications systems of an area) which provides the optimum service to the user in terms of cost and quality of service. As the number of regions in which the user wishes to be able to operate increases, so does the number of different communications systems that the subscriber station must attempt to acquire. The present invention provides a method and apparatus for selecting the communication system best suited to the user's needs.
The present invention is described in a multi-mode subscriber station, such as is described in detail in copending U.S. Pat. No. 5,754,542, entitled "METHOD AND APPARATUS FOR SYSTEM DETERMINATION IN A MULTI-MODE SUBSCRIBER STATION", which is assigned to the assignee of the present invention and is incorporated herein by reference. The exemplary embodiment is illustrated in the context of a subscriber station capable of transmitting and receiving CDMA signals and capable of transmitting and receiving analog signals, such as AMPS and NAMPS. The present invention is equally applicable to any digital communication system including TDMA, FDMA and GSM. In addition, the present invention is equally applicable to subscriber stations capable of operation in only one mode (e.g. analog or digital).